The Queen might enjoy the best conditions for her celebrations watching the Derby at Epsom on Saturday before outbreaks of rain spread in from the south-west.

Boats heading down the Thames on the river pageant through the capital on Sunday might be heading into a breeze for much of their journey, and participants and spectators will be hoping persistent rain expected across the southern UK holds off until the evening.

Maximum temperatures in London are likely to be around 14C (57F), while street party organisers across much of England, Wales and Northern Ireland will be keeping their fingers crossed. The weather in the UK's north-eastern corner looks more settled. UK averages for the time of year are around 17C, 18C in England.

On Monday, when Buckingham Place hosts an evening concert with stars from at least five of the Queen's six decades on the throne, there are likely to be a story of showers and bright spells, although temperatures could be slightly warmer.

The forecast for London and the south-east on Tuesday is again sunshine and showers with the possibility of occasional longer spells of rain, so the decision on whether the Queen travels in an open-topped Landau or covered coach for another procession – this time on roads – may have to be made at the last minute.

Dan Williams, of the Met Office, said: "It is quite complex weather for the latter part of the weekend. There are quite a number of different pressure systems – two highs either side of side of us, two lows north and south." That could mean a south-west, north-east split. Dry and cool in the north east, and more unsettled in the rest of the country.